Fix PyEnv Windows path calculation for environment grouping

[Copilot]

• Fix nativeToPythonEnv in pyenvUtils.ts - extract getPyenvDir helper
• Address reviewer feedback: use PYENV_ROOT env var as primary source, revert 3-levels-up to 2-levels-up (old behavior was correct for pyenv-win since versions live under ~/.pyenv/pyenv-win/versions/)
• Fix POSIX test to use absolute path with path.sep
• Add test for PYENV_ROOT preference
• Validate changes compile and all 583 tests pass (no regressions)
• Run code review and security scan

Original prompt

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This section details on the original issue you should resolve

<issue_title>PyEnv: Windows path calculation bug causes environment grouping to fail</issue_title>
<issue_description>## Problem

In pyenvUtils.ts, the calculation of versionsPath and envsPaths is incorrect on Windows due to the pyenv-win directory structure.

Current Code

// pyenvUtils.ts L128-130
const versionsPath = normalizePath(path.join(path.dirname(path.dirname(pyenv)), 'versions'));
const envsPaths = normalizePath(path.join(path.dirname(versionsPath), 'envs'));

Issue

On Windows, pyenv is located at ~/.pyenv/pyenv-win/bin/pyenv.bat. The current logic calculates:

• path.dirname(path.dirname(pyenv)) → ~/.pyenv/pyenv-win ❌
• Should be ~/.pyenv to find versions folder properly

This causes:

1. Environment grouping (PYENV_VERSIONS vs PYENV_ENVIRONMENTS) to fail
2. Environments not being associated with the correct manager

PET Server Reference

The PET server handles this correctly with platform-specific code in pet-pyenv/src/environment_locations.rs:

#[cfg(windows)]
pub fn get_home_pyenv_dir(env_vars: &EnvVariables) -> Option<PathBuf> {
    let home = env_vars.home.clone()?;
    Some(norm_case(home.join(".pyenv").join("pyenv-win")))
}

Suggested Fix

Add Windows-specific handling when calculating the versions and envs paths:

const pyenvDir = isWindows() 
    ? path.dirname(path.dirname(path.dirname(pyenv))) // Go up 3 levels on Windows
    : path.dirname(path.dirname(pyenv));
const versionsPath = normalizePath(path.join(pyenvDir, 'versions'));

Affected File

src/managers/pyenv/pyenvUtils.ts</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes PyEnv: Windows path calculation bug causes environment grouping to fail #1180

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[karthiknadig]

The core fix (extracting getPyenvDir with platform-aware logic) is a good idea, but I'm concerned the 3-levels-up calculation on Windows may produce the wrong root directory for environment grouping. Please verify what info.prefix the PET server returns for pyenv-win environments — if prefixes are under ~/.pyenv/pyenv-win/versions/, then versionsPath should also be computed relative to ~/.pyenv/pyenv-win, not ~/.pyenv.

[Copilot]

The core fix (extracting getPyenvDir with platform-aware logic) is a good idea, but I'm concerned the 3-levels-up calculation on Windows may produce the wrong root directory for environment grouping...

You were right — pyenv-win prefixes are under ~/.pyenv/pyenv-win/versions/, so the 2-levels-up calculation is correct. I've reverted that and now use PYENV_ROOT as the primary source, falling back to 2-levels-up. Fixed in 12033b0.

[karthiknadig]

LGTM! The updated approach is much better — using PYENV_ROOT as the primary source and keeping a consistent 2-levels-up fallback avoids the fragile platform-specific directory counting. Tests cover all three cases well.